Vitrectomy surgery has been successfully employed in the treatment of certain ocular problems, such as retinal detachments, resulting from tears or holes in the retina. Vitrectomy surgery typically involves removal of vitreous gel and may utilize three small incisions in the pars plana of the patient's eye. These incisions allow the surgeon to pass three separate instruments into the patient's eye to affect the ocular procedure. The surgical instruments typically include a vitreous cutting device, an illumination source, and an infusion port.
Current vitreous cutting devices may employ a “guillotine” type action wherein a sharp-ended inner rigid cutting tube moves axially inside an outer sheathing tube. When the sharp-ended inner tube moves past the forward edge of a side port opening in the outer sheathing tube, the eye material (e.g. vitreous gel or fibers) is cleaved into sections small enough to be removed through the hollow center of the inner cutting tube. Vitreous cutters are available in either electric or pneumatic form. Today's electric cutters may operate within a range of speeds typically between 750-2500 cuts-per-minute (CPM) where pneumatic cutters may operate over a range of speeds between 100-2500 CPM. The surgeon may make adjustments to control the pneumatic vitrectomy surgical instrument cutting speed, i.e. controlling the cutting device within the handpiece, in order to perform different activities during the corrective procedure. Corrective procedures may include correction of macular degeneration, retinal detachment, macular pucker, and addressing eye injuries.
The cutting device within a pneumatic handpiece requires precise control of applied pressure to overcome the internal spring return mechanism to assure the quality of each cutting stroke. Today's systems typically employ a constant opening signal time to open the valve at low cutting speeds. As the selected cutting speed increases, reducing the amount of time the valve is opened is often necessary to prevent constant over-pressurizing of the handpiece at the forward end of the cutting stroke. The frequency of opening and closing the pneumatic valve, i.e. the time interval between each opening cycle of the valve, is varied to achieve the desired cutting speed.
Although most designs use variable valve opening timing and variable timing between valve openings for pneumatic vitrectomy cutter control, certain advanced designs vary the input pneumatic supply pressure as vitrectomy cutter speed changes. Such operation can enhance the quality and efficiency of material processed by the vitrectomy cutter during each cut cycle. The fundamental limitation of a variable input supply pressure vitrectomy cutter control is the shortest amount of time that the air volume in the cutter body and the associated tube set may be pressurized to reach the minimum peak pressure required to advance the cutter to a cut position and then vent to reach the minimum residual pressure to allow the spring-loaded cutter to return to a retracted position. Again, current pneumatic designs are limited to cutting speeds within a range of approximately 100 to 2500 CPMs.
Further, current vitrectomy systems typically compensate for mechanical delays by providing excess pressure to extend the cutter and/or allocating excess time to retract the cutter. This type of operation is based on historical performance and some conjecture that the present situation is similar to past situations. Such operation and use of power and/or timing buffers are not optimal. Further, a certain amount of material is typically brought into the cutter based on the aspiration rate and the amount of time the cutter is open or closed, which is related to the pressure supplied to the cutter during each cut cycle. Such designs cut based on scheduled timing, resulting in more or less material cut than desired.
Today's vitrectomy surgical systems require a wide range of selectable cutting speeds and highly accurate control of the amount of pressure supplied is desirable to ensure proper instrument handpiece control and safe use in an operating theater. It may be beneficial in certain circumstances to offer the surgeon enhanced accuracy in cutting speeds, cutting efficiency, controllability, and other attributes related to performance of the vitrectomy procedure. Further, in certain circumstances benefits may be obtained by adjusting operation based on conditions encountered rather than establishing and employing operational parameters irrespective of such conditions, including altering operational parameters such as cut rate, amount of material cut, and other critical vitrectomy parameters.
Based on the foregoing, it would be advantageous to provide a system that enables pneumatic cutting functionality at cutting speeds at or higher than those achievable with today's vitrectomy surgical instrument systems. Such a design would benefit from options offered that provide more effective and efficient cutting parameters as compared with prior designs.